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Colorectal Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Overview

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Harms

Based on solid evidence, harms of postmenopausal combined estrogen plus progestin hormone use include increased risk of breast cancer, coronary heart disease, and thromboembolic events.

Magnitude of Effect: The WHI showed a 26% increase in invasive breast cancer in the combined hormone group, a 29% increase in coronary heart disease events, a 41% increase in stroke rates, and a twofold higher rate of thromboembolic events.

Study Design: Evidence from RCTs.
Internal Validity: Good.
Consistency: Good.
External Validity: Fair.

Polyp removal

Benefits

Based on fair evidence, removal of adenomatous polyps reduces the risk of CRC. Much of this reduction likely comes from removal of large (i.e., >1.0 cm) polyps, while the benefit of removing smaller polyps—which are much more common—is unknown. Some but not all observational evidence indicates that this reduction may be greater for left-sided CRC than for right-sided CRC.[24,25,26]

Magnitude of Effect: Unknown, probably greater for larger polyps (i.e., >1.0 cm) than smaller ones.

Study Design: Evidence obtained from cohort studies and one RCT of sigmoidoscopy.[25]
Internal Validity: Good.
Consistency: Consistent.
External Validity: Good.

Harms

Based on solid evidence, the major harms of polyp removal include perforation of the colon and bleeding.

Magnitude of Effect: Seven to nine events per 1,000 procedures.

Study Design: Evidence from retrospective cohort studies.[29,30]
Internal Validity: Good.
Consistency: Good.
External Validity: Good.

Diet modification

A diet low in fat and meat and high in fiber, fruits, and vegetables

Benefits

Based on fair evidence, a diet low in fat and meat and high in fiber, fruits, and vegetables started as an adult does not reduce the risk of CRC by a clinically important degree.

Study Design: Evidence obtained from pooled analyses of multiple cohort studies and RCTs.
Internal Validity: Fair, but measurement error is a potential problem.
Consistency: Some inconsistency, with one large pooled study [31] finding a reduced risk of distal colon cancer associated with fruit and vegetable intake. RCTs have been consistent.
External Validity: Good, studies have included large population-based studies.

Harms

There are no known harms from dietary modification, including reduction of fatty acids or meats and an increase in the intake of fiber, fruits, and vegetables.

Study Design: Cohort and RCT's.
Internal Validity: Good.
Consistency: Good.
External Validity: Good.

Calcium supplementation

Benefits

The evidence is inadequate to determine whether calcium supplementation reduces the risk of CRC.

Study Design: Pooled and individual prospective cohort studies, meta-analysis of three RCTs with adenoma recurrence as an outcome, and one large individual RCT in women with CRC as an outcome.
Internal Validity: Good.
Consistency: Poor; the RCT with CRC as an outcome [32] found no reduction in CRC incidence, while prospective cohort studies found a reduction in CRC incidence between high and low calcium groups; three RCTs found a reduction in adenoma recurrence with calcium supplementation.[33]
External Validity: N/A.
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WebMD Public Information from the National Cancer Institute

Last Updated: February 25, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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